Nano-enabled Energy Conversion, Storage and Thermal Management Systems (NEXT) Group

University of Colorado at Boulder

 

Director: Dr. Ronggui Yang, Assistant Professor of Mechanical Engineering

Office Location: ECME 136, Engineering Center

Post-Doctor Offices: ECME 251A, ECME 251B

Student Offices and Labs: ECME 165, ECME 219, ECME 1B80

Tel: 303-735-1003 (O),  303-735-1763  (Lab);  Fax: 303-492-3498

 

 

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Currently our research spans over developing numerical/theoretical and experimental tools for understanding nanoscale thermal transport, probing new transport phenomena in nanocomposites, hybrid inorganic-organic crystals, and hybrid micro/nano-structures, and applying the discoveries in fundamental sciences at micro/nano-scales to thermal management and energy conversion/storage systems. To better reflect the expertise and the research activities of our multi-disciplinary research team, we recently re-named our “Nanoscale and Ultrafast Thermal Sciences and Applications (NUTS)” group built in January 2006 to “Nano-enabled Energy Conversion, Storage, and Thermal Management systems (NEXT)” group.

 

A) SELECTED RESEARCH AREAS:

 

1. Modeling and Simulation of Nanoscale Thermal and Thermoelectric Transport:

As the size of structures approaches the nanoscale, the conventional Fourier law of heat conduction does not remain applicable. We are interested in understanding how heat transfer in nanostructures differs from that in macrostructures and how to model and predict the heat transfer in nanostructures. We have developed the deterministic (discrete ordinate method and finite volume method) and stochastic (Monte Carlo) simulation tools based on the Boltzmann transport equation. These tools have been very widely used or re-produced by researchers all over the world. In particular, we have used the tool to study the hot spot phenomena in nanoscale MOSFETs, the workhorse of microelectronics, and to predict the thermal conductivity of semiconductor core-shell nanowires and nanocomposites, which has led to the significant advances in thermoelectrics. Our current work focuses on multiscale and multi-carrier modeling and simulation by effectively integrating multiscale simulation tools, which enables us to study the fundamental thermal transport processes in nano/microscale structures and perform multiscale simulations of the thermal transport processes in devices and systems containing embedded nanostructures. On the atomic-scale end, we are trying to integrate atomic simulations including molecular dynamics, nonequilibrium Green’s function theory, and first principles calculation with the Boltzmann transport equation-based simulation tools. On the macroscale, we are trying to integrate the Boltzmann equation tools with conventional Fourier heat conduction law and the design/optimization tools.

 

2. Soft X-ray for Probing Nanoscale and Ultrafast Thermal Transport:

Femtosecond laser is a unique tool to study a number of ultrafast relaxation processes and nanoscale phenomena. We have constructed a femtosecond two color (blue & near-infrared) pump-probe system with 8 ns delay time with the aim to extract the phonon relaxation time and phonon reflectivity at interfaces which are essential parameter inputs for nanoscale thermal transport modeling/simulations. This experiment system is now on daily operation for studying electron energy relaxation, phonon energy relaxation, and electron-phonon coupling in bulk and nanostructured materials. Collaborating with ourphysics colleagues Professor Margaret Murnane and Professor Henry Kapteyn of JILA/physics at CU-Boulder, we have been constructing a pump-probe system using the table-top femtosecond soft X-ray beams. The soft X-ray offers many advantages over visible or infrared light due to its short wavelength (selective wavelength of 2-30nm). We have recently used the change in diffraction from micro/nanostructured gratings to directly observe the transition between diffusive and ballistic heat transport. The initial report of this groundbreaking work in CLEO conference has attracted a lot of interest and was highlighted as one of the 5 CLEO Technical News Summaries (May 2008) and later was highlighted again as one of the 4 Physics Update items in the July 2008 issue of Physics Today, the membership magazine of the 120,000-member American Institute of Physics. p.17 (July 2008). Very recently, a journal paper reporting this experimental observation has been accepted by Nature Materials.

 

The experimental system we developed enables us to further understand nanoscale and ultrafast thermal transport fundamentals. Currently we focus on demonstrating the possibility of using soft X-ray to image thermal transport with nanoscale spatial and picosecond temporal resolutions simultaneously. The success of such an implementation will enable us to watch how thermal energy is dissipated in the drain side of nanoscale transistors, how the heat is propagated through an interface of dissimilar materials, how the heat is generated and transported surrounding nanoparticles in a variety of environment.

3. Micro/Nano-Enabled Thermal Management

The scaling down of feature sizes in microelectronic devices leads to an increase in heat dissipation per unit volume that consequently may affect device performance and reliability. A very similar concern arises in the design of high power semiconductor lasers in which heat generation can become extreme. Further, the energy conversion technologies also rely on efficient thermal management. For example, the external thermal management solutions boost the efficiencies of thermo-photovoltaics and solar cells by increasing the heat removal capability. Nanotechnology not only creates hurdles but also solutions for thermal management. Working with our colleagues Professor YC Lee, Professor Victor Bright and Professor Steven George of CU-Boulder and Professor Chen Li and Professor G.P. Peterson, we conceptualized the possibility to build flexible thermal ground planes that have 100 times better thermal conductivity than diamond, the best natural thermal conducting material, by utilizing phase change heat transfer in hybrid micro/nano- wicking structures encased in millimeter-thick polymer chamber. Such an innovation will enable a new generation of high-performance, integrated microelectronic, power conversion, photonic or microwave systems operating at high power density without constraints resulting from complex thermal management solutions. The key to our innovation is manufacturable micro/nanotechnologies for low-cost applications and the in-depth understanding of phase change heat transfer. We will significantly further the understanding of how micro/nano-structures could improve phase change heat transfer by this study.

 

4. Nano-Enabled Energy Conversion and Storage:

One of our most successful applications in tailoring transport properties is nano-thermoelectrics, for which we use nanotechnologies to engineer structures to have thermal conductivity lower than alloys while maintaining electron power factor (electrical conductivity times the square of thermoelectric Seebeck coefficient), which is not achievable in bulk materials. Collaborating with Professor Gang Chen and Professor Mildred Dresselhaus who are pioneers in nanostructured thermoelectrics, we laid out the theoretical foundation for proposing nanocomposites as high efficient thermoelectric materials during my Ph.D study at MIT. Our nanocomposite work brought in a paradigm-shift to thermoelectric research from the proof-of-concept demonstration to a potential commercial product since nanocomposites can be cost-effectively fabricated to realize nano-enabled efficiency enhancement. Our current work on thermoelectrics include: 1) modeling and characterization of various thermoelectric nanostructures, 2) developing atomic-layer deposition-enabled low-cost thermoelectric nanocomposites that are low-cost but could potentially have similar efficiency as superlattices, 3). developing integrated thermoelectric systems for solar-electricity, waste heat recovery and thermal management. In addition, we are also collaborating with Professor Se-Hee Lee on core-shell silicon nanowires for lithium ion battery electrode applications. An interesting project we are pursuing is the on-chip integration of silicon-nanowire array-enabled photovoltaic and lithium ion batteries which could provide potentially 24-hour uninterrupted solar power-supply.

 

B). RESEARCH AWARDS (to PI Professor Ronggui Yang):

2009-2014 National Science Foundation (NSF) CAREER Award (the National Science Foundation's most prestigious awards in support of junior faculty who exemplify the role of teacher-scholars through outstanding research, excellent education and the integration of education and research within the context of the mission of their organizations.)

2009 Selected as one of the <100 Invited Participants, the US National Academy of Engineering's (NAE) 15th U.S. Frontiers of Engineering Symposium.

2009 Biography featured as a technology developer with outstanding potential that could reverse the decline in the book “The Decline of American Technology” by Dr. Lynn G. Gref, to be published in Spring 2010.

2008 Technology Review’s TR35 Award (one of the 35 young scientists and technologists in world who are under the age of 35, but their work--spanning medicine, computing, communications, electronics, nanotechnology, energy, and more--is changing our world.)

2008 DARPA/MTO Young Faculty Award (one of the 39 rising stars in university microsystems research)

2008-2011 Sanders Faculty Fellow, College of Engineering and Applied Science, CU-Boulder.

2008 Outstanding Research Award, Department of Mechanical Engineering, CU-Boulder

2008 Nominated for IEEE/ACM William J. McCalla ICCAD 2008 Best Paper Award by the conference organizers of the 2008 International Conference on Computer-Aided Design (ICCAD).

2005 Best Paper Award – Research, InterPACK 2005 (the ASME/Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems), 1 out of 500+ papers.

2005 Goldsmid Award for Excellence in Research in Thermoelectrics, International Thermoelectrics Society.

2004 NASA Certificate of Recognition for a Technical Innovation (Space Act Tech Brief Award), NASA Inventions and Contributions Board.

2003 Elected full member of Sigma Xi, the Scientific Research Society.

 

C) RESEARCH FUNDING

1.      CAREER: An integrated research and education program on nanoscale thermal transport: developing a high spatiotemporal resolution photo-thermal microscope, National Science Foundation, PI: Ronggui Yang, $400K + $60K (university matching), 02/01/2009-01/31/2014.

2.      Novel Silicon/NixSn1-x Core-Shell Nanowires for Superior High Capacity and Long Lifetime Lithium-Ion Batteries, PI: Ronggui Yang, Co-PIs: Se-Hee Lee and Wei Wang, University of Colorado Innovative Seed Grant, Total: $41,200, 07/01/2009-06/30/2010.

3.      A micro-scale hybrid wick heat pipe cooling system for high concentration photovoltaic cell, University of Colorado Technology Transfer Office Energy Initiative Proof of Concept Grant, PI: Chen Li, Co-PIs: Victor M. Bright, Ronggui Yang, Y.C. Lee, Total: $50K, Yang: $0, 04/01/2009-03/31/2010.

 

4.      Modeling and experiments in the nucleate boiling regime in the context of power electronics cooling, National Renewable Energy Lab, PI: Ronggui Yang, $175K, 10/01/2008-09/30/2011.

5.      Surface Plasmon Enabled High Efficiency Thermoelectric Devices, DARPA MTO Young Faculty Award, PI: Ronggui Yang, $150K, 06/01/2008-11/30/2009.

6.      A Design tool for nanostructures with tunable thermal properties, AFOSR (BAA 2007-08 Discovery Challenge Thrusts), PI: Ronggui Yang, Co-PIs: Kurt Maute and Martin Dunn, $600K, 03/01/2008-12/31/2010.

7.      Flexible thermal ground plane with micro/nano wicking structures, DARPA (BAA 07-36 Thermal Ground Plane), PI: Y.C. Lee, Co-PI: Ronggui Yang, Chen Li, Victor Bright, G.P. “Bud” Peterson, and Suraj Rawal, $4.0M, 04/01/2008-12/30/2011.

8.      Nanowire-based metamaterials for miniaturized antennas, DARPA iMINT Center Seed Grant, PI: Won park, Co-PIs: Ronggui Yang, Y.C. Lee, and Pavel Kabos, T. Mitch Wallis, Jim Booth, Total: $50K, Yang; $0, 04/01/2008-03/31/2009. completed

9.      MRI-Consortium: Acquisition of a Supercomputer by the Front Range Computing Consortium, National Science Foundation (Award #0821794), one of ~50 CU Faculty Participants with PI Henry Tufo, $2.8M, Yang: $0, 8/1/2008 - 7/31/2012.

 

10.  Nanocomposite thermoelectric materials development and characterization, Lockheed Martin Corporation, PI: Ronggui Yang, $50K, 10/25/2007-11/15/2008. completed

11.  A design-centered approach to nano-engineering, National Science Foundation, PI: Kurt Maute, Co-PIs: Martin Dunn and Ronggui Yang, $329,957, 09/01/2007-08/31/2010, 0.25 summer month.

12.  Understand the building with your eyes: building and environment science and technology visualization Lab. CU-Engineering Excellence Fund, co-PI with John Zhai. $26,695, 05/01/2007-04/01/2008. completed

13.  Unrestricted gift fund, $6,000, 10/15/2007 ~.

 

14.  Energy harvesting and storage systems and their integration into AF aero vehicles, Air Force Office of Scientific Research - Multidisciplinary University Research Initiative (AFOSR-MURI); PI: Minoru Taya, Co-PI with 8 other co-PIs, total: $6M, CU: $1.50M, Yang: $500K, 05/01/2006-04/30/2011.

15.  Measurement of thermal transport in nanostructures using EUV pump-probe systems, National Science Foundation; PI: Ronggui Yang (Funded through the NSF Engineering Research Center for Extreme Ultraviolet Science and Technology - NSF EUV ERC), $50K annually, 05/01/2006-09/30/2013.

16.  Constructing a femtosecond nanometer resolution photo-thermal imaging system using extreme ultraviolet (EUV) to study nanoscale thermal transport, National Science Foundation; PI: Ronggui Yang, Co-PI: Margaret Murnane, $94,919, 09/01/2006-08/31/2007. completed

17.  Photonic crystal fiber based micro capillary pumped loops, CU Technology Transfer Office Proof of Concept Grant (POCg); PI: Ronggui Yang, $12,500, 12/01/2006-05/31/2007. completed

18.  Photonic crystal fiber based micro heat pipe arrays and capillary pumped loops, CU Engineering Dean’s Seed Fund for Novel Ideas; PI: Ronggui Yang, Co-PIs: Y.C. Lee and Victor M. Bright, $10,000, 06/10/2006-12/31/2006. completed

19.  Unrestricted gift fund, $15,000, 08/15/2006 ~.

20.  University of Colorado Start-up Funds: Equipments + Discretionary, PI: Ronggui Yang, $410K + student support, 01/2006 – 01/2009, completed.